It is a common requirement in many mechanisms to convert a rotating motion into a reciprocating motion or a reciprocating motion into a rotating motion. Typical examples of this requirement are internal combustion or steam engines and cutting or stamping machines. It is common practice to achieve the conversion using cranks and crankshafts or Scotch Yokes. However, such devices require considerable space, usually in the axis of the reciprocating motion and are therefore inconvenient, particularly in small hand-held devices such as electric brushes. Thus, there is a need for a compact, lightweight mechanism to achieve the conversion, particularly for use in small hand-held devices.